I've replaced the original non-posi rear drum braked rear end in my 92RS with a 87 nine bolt posi with disc brakes. I installed a new GM disc/disc combination valve as well as rebuilt rear calipers. Now, my pedal goes down about 3/4 to the floor before any real braking action begins. Yo, throw out the anchor! Push the pedal down hard and fast, and the brake warning light comes on and stays on till I pump the pedal. The master cylinder seems to hold pressure, especially when the pedal is pumped, all the lines look good, I've bled the system twice, not spungy. Any suggestions / ideas? Thanks.

 

I recently had a similar problem after working on my rear discs. I didn't have the brake light come on, but the pedal went down real far before anything would happen. I took the car in for an alignment and asked them to adjust the parking brake...problem solved. I didn't think adjusting the parking brake would make such a difference but it did (unless they did something else I didn't know about). I may skip adjusting it on my own in the future.

 

Parking brake adjustment... you could be right! Hadn't thought about that. Thanks for the tip.

 

After the fourth session of bleeding the entire system I have brakes. Guess it was just as simple as that... I should have known better and been a whole lot more patient.